Art of mounting crystal detectors



Dec. 24, 1946. w LA RUE ART OF MOUNTING CRYSTAL DETECTORS Filed Feb. 28, 1942 3 a 1 a a 9 Snnentor Rue VViZliam B. La

Gttomeg Patented Dec. 24, 1946 ART OF MOUNTING CRYSTAL DETECTORS William D. La Rue, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1942, Serial No. 432,818

This invention relates to the art of mounting silicon, galena and similar detector crystal elements for use in the rectification or demodulation of radio frequency oscillations.

The sensitivity of the usual crystal detector is confined to a number of unpredictable spots on its surf-ace and, in order to locate these sensitive punctiform areas, it is customary to so mount the spring. wire (cat whisker) contact that it is susceptible of movement to any part of the surface of the crystal. Such mounts usually comprise an arm supported in a ball and socket joint which may be adjusted to vary the pressure of the contact on the crystal when a sensitive spot has been located. Though it is entirely possible to provide means for locking the joint and hence the supporting arm in a desired position, the force applied to the crystal through this contact will usually vary with time or with atmospheric conditions or by reason of shocks or tremors of external origin. Further, such mounts are cumbersome and usually require the use of auxiliary wires and binding posts which may inhibit their use in connection with circuits designed to transmit oscillations of ultra high frequencies.

Accordingly, the principal object of the present invention is to provide an extremely compact and trouble-free holder for a crystal of the general character described, and one incorporating a simple and reliable means for adjusting the position and pressure of the contact element upon the crystal.

Another object of the invention is to provide an improved crystal holder which may be connected without the use of auxiliary wires to modcm high frequency apparatus such, for example, as a concentric transmission line.

Other objects and advantages, together with certain preferred details of construction, will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawing wherein:

Fig. 1 is a vertical sectional View, partly in elevation, showing a crystal holder constructed in accordance with the present invention and mounted for use;

Fig. 2 is a view similar to Fig. 1, but with the holder rotated 90;

Fig. 3 is an exploded view, partly in section, of the crystal holder shown in Figs. 1 and 2 and including a separate adjusting tool;

Fig. 4 is an enlarged transverse section taken on the line 4--4 of Fig. 1; and

Fig. 5 is an enlarged transverse section taken on the line 5-5 of Fig. 2.

5 Claims. (Cl. 250-31) In the drawing, wherein like reference characters designate the same parts in all figures, the invention is shown as applied to the mounting of a silicon crystal l which, in the instant case is provided with a cuneiform detector surface la. This wedge-shape crystal I is mounted in a small metal cup 3 with the crystal partly embedded in some soft metal 5, such as Woods metal. The cup 3 is provided with an outwardly extending peripheral flange 3a and is here shown as terminating in a dependent prong 31). for engagement with a female socket element 1 which, for certain applications, may comprise a suitable apertured inner-conductor 9 of a transmission line or tank circuit whose other or outer conductor is indicated at I l in Figs. 1 and 2.

The flange So on the cup 3, which holdsthe crystal l, serves as a seat for a hollow cylinder or tube 13 which is preferably constituted of Lucite (methyl-methacrylate resin), glass, or other transparent material, to permit observation of the crystal l and its later described contact element 2|. This tube l3 terminates at its other end in a metal sleeve or bushing l5 which has a lower end zone lEa of reduced thickness, which permits it to be seated snugly within the upper end of the tube, central zone b of a diameter corresponding to the diameter of the said tube, and an upper zone |5c which is provided with a circumferential shoulder 15d which, as shown in Figs. 1 and 2, may serve as a conductive seat for the holder when it is connected in circuit. Cement may be used at the ends of the transparent tube 13 to provide a hermetic seal between it and its oppositely located metal terminal members 3 and I5.

A solid metal piston or plug H which, is provided at its upper end with a threaded bore He for engagement with a complementarily threaded adjusting tool l9, serves as a support for the spring wire cat whisker contact 2!. This contact element 2| may be attached to the plug [1 as by staking its upper end within a slot I'ls, provided for the purpose, adjacent the periphery of the plug.

The spring wire contact 2| is designed espe-' cially for use with the wedge-shape silicon crystal I, here illustrated, that is to say, it comprises a vertical portion '0, and a horizontal arm h which may be biased in the direction of the crystal by a connecting loop 0. Since the upper end of this spring wire contact 2| is attached adjacent the periphery of the plug ll, it is obvious that when the plug is moved downwardly within its bushing I5, as by pressure applied to the knurled end k of the adjusting tool l9, to a position whereat the horizontal contact arm it touches the crystal I, the said arm may then be caused to "wipe the ridge to of the crystal (to locate a sensitive area thereon) simply by rotating the said plug l1, and hence the said arm, by means of the adjusting tool It.

Assuming that the adjusting tool I9 is provided with a right-hand thread, it is apparent that the plug I! and the contact arm 72. can be moved only in a clockwise direction (as indicated by the ar row in Fig. 4) and that turning the tool 19 in a counter-clockwise direction will serve to unscrew and disengage it from its threaded seat He in the upper end of the plug ll.

It will be observed upon inspection of Figs. 1, 3 and 4 that the plug or piston H has a slot llt therein, which extends axially from its inner extremity to a point say midway of its length. This axial slot l'lt fulfills two important functions: (1) it serves to bias the bifurcated surface of the plug into engagement with the inner surface of the bushing [5 with sufiicient force to prevent rotation of the contact element 2| when the removable adjusting tool I9 is screwed in the direction necessary to effect its removal and (2) since the said slot extends to the leading end of the plug and biases the said end into intimate contact with the bushing l5 adjacent that end. it serves to establish the shortest practical electrical path between the crystal l and the external circuit element II. This latter feature is of especial significance when the crystal is employed in the rectification or demodulation of oscillations of extremely high frequencies, since it in no wise increases the effective inductance of the circuit.

As above indicated, the holder here illustrated is so constructed that the adjusting tool [9 may be withdrawn without disturbing the position of and/or the pressure exerted by the spring wire contact arm h on the beveled edge Id of the crystal I. Subsequent to the removal of the adjusting tool l9, the holder may be permanently sealed against dust and moisture by a filling 2| of a suitable cement or the like which may be capped, if desired, by a metal seal or identification disc 23.

Various modifications of the invention will suggest themselves to those skilled in the art. It is to be understood therefore that the foregoing is to be interpreted as illustrative and not in a limiting sense except as required by the prior art and the spirit of the appended claims.

What is claimed is:

l. A device of the character described comprising an envelope containing a detector crystal, a metal sleeve having a bore which communicates with the interior of said envelope, a piston in the bore of said sleeve, a contact element for said crystal mounted on said piston adjacent its inner end, means of low effective impedance for biasing the wall of said piston into engagement with the inner surface of said sleeve, and means for moving said piston and hence said contact element into engagement with a surface of said crystal against the force of said biasing means.

2. The invention as set forth in claim 1 wherein said metal sleeve extends to the exterior of said envelope and comprises means for connecting said device to an external circuit.

3. The invention as set forth in claim 1 and wherein the overall length of said piston and said contact element is less than the length of said sleeve and wherein the otherwise empty portion of the bore of said sleeve contains a sealing compound.

4. A device of the character described comprising an envelope containing a detector crystal, a metal sleeve having a bore which communicates with the interior of said envelope, a piston in the bore of said sleeve, a contact element for said into engagement with a selected surface area of said crystal, and means of low effective impedance adjacent the inner end of said piston for inhibiting displacement of said piston and hence of said contact element when said adjust- I ing movement ceases.

. in said envelope and adapted to be moved into and out of engagement with said crystal surface as determined by the direction in which said piston is moved, said piston comprising a metal cylinder having a threaded socket on its outer end adapted to receive a complementarily threaded adjusting tool and having a bifurcated portion adjacent one of its ends, the bifurcated portion of said cylinder being biased to engage the inner surface of said sleeve whereby to inhibit relative movement therebetween when said adjusting tool is turned in a direction calculated to effect its removal from said threaded socket.

WILLIAM D. LA RUE. 

